1. Field of the Invention
This invention relates to roller blinds with a horizontally oriented winding shaft and more particularly refers to a blind with a safety device which blocks the winding shaft in the event of a failure of the support or driving means and arrests unrolling.
2. Description of the Prior Art
Rolling gates and roller blinds with horizontal winding shafts, hereinafter collectively referred to as roller blinds, are known in the art. Unfortunately, failure of the driving mechanism or other support controlling the unrolling of the blind would occur with the result that the blind would make a rapid descent attaining considerable gravitational momentum placing great stress on the parts of the roller blind and often causing appreciable damage to it.
The known safety devices to arrest the winding shaft of the roller blind rely on the use of centrifugal force, which depends on the speed of rotation of the shaft, and requires that it reach a predetermined value which exceeds that of the normal unrolling speed. A necessary condition for this safety device to respond is therefore a sufficient height of fall of the roller blind, that is a height required for the build-up of the necessary centrifugal forces. However, this necessary falling distance which is considerable may already lie in the danger range. In addition, the safety device can be damaged or destroyed by the gravitational momentum of the already unrolled portion of the roller blind.